Useful Links For Unix and Linux:

Linux for the Desktop

Fedora
Fedora Core is derived from the original Red Hat Linux distribution, and it is aimed towards home users.

Ubuntu
Ubuntu is based on the GNOME desktop environment, which is intended to provide a free, simple and intuitive interface while offering a full range of modern desktop applications.

Linux for the Server

CentOS
Community supported distribution which aims to be 100% compatible with Red Hat Enterprise Linux without Red Hat branding and various non-free software.